The air environment in the subway car has a great impact on the comfort and health of passengers. In order to know the real air quality in the car when the train is running, this paper takes CO2 as ...an indicator and conducts a field test on Line 11 of Shanghai Metro to study and analyse the dynamic CO2 concentration and the fresh air rate in the subway car. The results show that the CO2 concentration increases from the head car to the tail car, and the fresh air volume decreases from the head car to the tail car is the reason for the large difference of CO2 concentration in different cars. The CO2 concentration in the car is greatly affected by the passenger load, and the maximum value of CO2 concentration in the morning peak can reach 2.3 times that of the normal hours. The background CO2 concentration has a certain influence on the CO2 concentration in the car, and the CO2 concentration in the underground line is higher than that in the elevated line in the same carriage. The CO2 concentration in subway cars of the underground line in the morning peak is significantly higher than 1500 ppm, which indicates that the dilution effects of the ventilation can’t meet the fresh air requirements in the morning peak. The research in this paper can provide a reference for the design of the ventilation system of subway trains and the environmental control in the car.
Natural ventilation in relatively enclosed underground spaces has aroused people’s interest due to the poor air quality and high energy consumption of mechanical ventilation. Small-scale experiments ...and numerical simulation are utilized to investigate the influence of thermal and wind conditions on the ventilation characteristics of underground corridors. The non-dimensional flow rate is calculated, which can be used to evaluate ventilation performance and predict airflow rate. The interaction of driving forces is quantitatively analyzed based on the Archimedes number and the critical non-dimensional flow rate. The results reveal that incoming wind counteracts buoyancy partly in shear ventilation, while the wind promotes buoyancy-driven ventilation in cross ventilation. The air change rate decreases under different driving force modes, from the purely buoyancy-driven to the combined-force-driven to the purely wind-driven, for shear ventilation with the wind speed of 1 ∼ 3 m/s. For cross ventilation, the descending order is the combined-force-driven, the purely wind-driven, and the purely buoyancy-driven. When driven by wind, non-dimensional flow rate remains constant with a value of 0.025 for shear ventilation and 0.68 for cross ventilation in the corridors with the opening ratio less than 12 %. When driven by combined force, Q* is not a constant value but rather varies with wind speed. Especially when the wind speed exceeds 1.5 m/s, the buoyancy can be ignored in cross ventilation. The findings of this study can serve as a basis for ventilation design and the prediction of ventilation rate in underground corridors.
The air environment in the subway car has a great impact on the comfort and health of passengers. In order to know the real air quality in the car when the train is running, this paper takes CO
2
as ...an indicator and conducts a field test on Line 11 of Shanghai Metro to study and analyse the dynamic CO
2
concentration and the fresh air rate in the subway car. The results show that the CO
2
concentration increases from the head car to the tail car, and the fresh air volume decreases from the head car to the tail car is the reason for the large difference of CO
2
concentration in different cars. The CO
2
concentration in the car is greatly affected by the passenger load, and the maximum value of CO
2
concentration in the morning peak can reach 2.3 times that of the normal hours. The background CO
2
concentration has a certain influence on the CO
2
concentration in the car, and the CO
2
concentration in the underground line is higher than that in the elevated line in the same carriage. The CO
2
concentration in subway cars of the underground line in the morning peak is significantly higher than 1500 ppm, which indicates that the dilution effects of the ventilation can’t meet the fresh air requirements in the morning peak. The research in this paper can provide a reference for the design of the ventilation system of subway trains and the environmental control in the car.
Memristive system with infinitely many equilibrium points has attracted much attention for the generation of extreme multistability, whose initial-dependent dynamics can be interpreted in a ...reduced-order model through incremental integral transformation of state variables. But, the memristive system with any extra nonlinear terms besides the memristor ones cannot be handled directly using this method. In addition, the transformed state variables could be divergent due to the asymmetry of the original system. To solve these problems, a hybrid state variable incremental integral (HSVII) method is proposed in this paper. With this method, the extreme multistability in a four-dimensional (4D) memristive jerk system with cubic nonlinearity is successfully reconstituted in a three-dimensional (3D) model and the divergent state variables are eliminated through ingenious linear state variable mapping. Thus, mechanism analysis and physical control of the special extreme multistability can readily be performed. A hardware circuit is finally designed and fabricated, and the theoretical and numerical results are verified by the experimental measurements. It is demonstrated that this HSVII method is effective for the analysis of multistable system with high-order nonlinearities.
To better demonstrate the asymmetric properties of physical memristive devices, this paper presents an asymmetric memristor emulator that is constructed by an asymmetric diode-bridge cascaded with a ...parallel resistor–capacitor (RC) filter. By introducing this emulator into a third-order jerk circuit in both forward and reverse ways, this paper constructs two types of asymmetric memristor-based jerk circuits. The two circuits don’t have symmetry themselves, but they are symmetric with each other. By using multiple numerical methods, parameter-associated bifurcation behaviors and initial-associated coexisting behaviors are revealed. Complex dynamics can be thereby observed from these two circuits, including period, chaos, periodic bubble, chaotic bubble, period-doubling bifurcation, antimonotonicity, and extreme event. Furthermore, Multisim circuit simulation models are established and the measured results validate the numerically simulated ones.
Purpose
The purpose of this paper is to develop two types of simple jerk circuits and to carry out their dynamical analyses using a unified mathematical model.
Design/methodology/approach
Two types ...of simple jerk circuits only involve a nonlinear resistive feedback channel composited by a nonlinear device and an inverter. The nonlinear device is implemented through parallelly connecting two diode-switch-based series branches. According to the classifications of switch states and circuit types, a unified mathematical model is established for these two types of simple jerk circuits, and the origin symmetry and scale proportionality along with the origin equilibrium stability are thereby discussed. The coexisting bifurcation behaviors in the two types of simple jerk systems are revealed by bifurcation plots, and the origin symmetry and scale proportionality are effectively demonstrated by phase plots and attraction basins. Moreover, hardware experimental measurements are performed, from which the captured results well validate the numerical simulations.
Findings
Two types of simple jerk circuits are unified through parallelly connecting two diode-switch-based series branches and a unified mathematical model with six kinds of nonlinearities is established. Especially, the origin symmetry and scale proportionality for the two types of simple jerk systems are discussed quantitatively. These jerk circuits are all simple and inexpensive, easy to be physically implemented, which are helpful to explore chaos-based engineering applications.
Originality/value
Unlike previous works, the significant values are that through unifying these two types of simple jerk systems, a unified mathematical model with six kinds of nonlinearities is established, upon which symmetrically scaled coexisting behaviors are numerically disclosed and experimentally demonstrated.
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